1. Field of the Invention
The present invention relates generally to a changeover valve system and, more specifically, to a suitable and efficient three-way, changeover valve system that is adapted to be mounted on a pressurized piping system. The changeover valve system of the present invention is mounted on a single pipe riser in the pressurized piping system and includes at least two independent pressure relieving devices such as, for example, pressure relief valves. The changeover valve system is adapted to permit the transfer of the active pressure relieving function from one pressure relieving device to the other pressure relieving device during operation of the pressurized piping system without jeopardizing the pressure relieving capability of the pressurized piping system.
2. Description of the Prior Art
The prior art fails to specifically address either the problems or the solutions arrived upon by applicant. For example, Fetterolf Corporation has marketed a horizontal stem double-seated globe valve called a Ram-Seal Valve that provides a high pressure drop or resistance to flow. Due to its configuration, it is often necessary to use oversized valves to provide the required flow capacity. In addition, valves of this configuration have a large envelope size which limits their application.
In cases where a second changeover valve is connected to the outlet of the pressure relieving devices mounted on the first changeover valve in a tandem arrangement, there must be a simultaneous mechanical operation of the changeover valves in order to maintain the over pressure protection for the system.
With the Fetterolf and similar designs, it is difficult to coordinate the seating positions in a tandem arrangement and automation is difficult or impossible. Further, it is often difficult to seal long rising or multiple rotation stems.
One similar type valve is marketed by FEMA designated as Valvola di Scambio.
Anderson, Greenwood & Co. has marketed a changeover valve that utilizes a flat closure disc with a vertical "Y" type design. In such an arrangement, the valve stem must be driven down sufficiently to permit the disc to be rotated 180 degrees to the opposite seat and then retracted in an upward direction to close the disc to the scat. Such operation is complex and requires torque measuring devices to meet the manufacturer's operating specifications. The number of seem rotations required to raise and lower the disc and the 180 degree rotation required to change flow positions precludes the application of an integral manual operating handle.
Moreover, the multiple operations that are required (i.e., lowering, rotating and raising) effectively precludes remote actuation of a single valve and is even more complex in tandem applications.
Further, in such a design, the application of reverse pressurization to test the set pressure of the isolated pressure relief device tends to force the disc away from the seat and add loads to the operating mechanism. Therefore, it may not be possible to pressurize and test such pressure relieving devices in place when mounted.
Another example of a selector valve is described in U.S. Pat. No. 4,821,772 which issued on Apr. 18, 1989 to William L. Anderson, Jr., entitled Dual Active Selector Valve. The Anderson '772 patent describes the Anderson Greenwood valve previously discussed. In particular, it shows additional flow passages if more than one active pressure relieving device is desired.
Other examples of multiple outlet or shuttle valves include those described in U.S. Pat. No. 5,329,968 which issued on Jul. 19, 1994 to Walter W. Powell entitled Shuttle Valve and U.S. Pat. No. 4,403,626 which issued on Sep. 13, 1983 to Herman L. Paul, Jr. entitled Valve Assembly.
Examples of ball valves include those described in U.S. Pat. No. 5,251,663 which issued on Oct. 12, 1993 to Rollin C. Christianson et al. entitled High-Temperature, High-Pressure Oxygen Metering Valve; U.S. Pat. No. 4,915,133 which issued on Apr. 10, 1990 to C. L. Scott Harrison entitled Valve Device for Piping Systems; U.S. Pat. No. 4,881,718 which issued on Nov. 21, 1989 to Raymond P. Champagne entitled Ball Control Valve; U.S. Pat. No. 4,441,524 which issued to Hisayoshi Mese on Apr. 10, 1984 entitled Ball Valve; U.S. Pat. No. 4,203,572 which issued to Ronald D. Coffman on May 20, 1980 entitled Locking Ball Valve; U.S. Pat. No. 3,345,032 which issued on Oct. 3, 1967 to W. W. Rawstron entitled Three-Way Ball Valve; U.S. Pat. No. 3,537,473 which issued on Nov. 3, 1970 to David B. DeZurik, Jr. entitled Anti Slam Valve Positioning Means; U.S. Pat. No. 3,184,213 which issued on May 18, 1965 for Clifford E. Anderson entitled Seat For Top Entry Ball Valve; and U.S. Pat. No. 3,100,499 which issued on Aug. 13, 1963 to Harold E. Bass entitled Valve.
As will be appreciated, none of the valve systems heretofore described teach or suggest the use of a three-way, changeover valve that offers the unique advantages presented by the changeover valve system of the present invention.